This invention relates to an oscilloscope with a simplified setup procedure and to a procedure for setting up an oscilloscope.
An oscilloscope can be used to display a waveform representing change of a first variable as a function of a second variable. It will be convenient in the following discussion to assume from time to time that the first variable is the magnitude of a measured quantity, expressed as a voltage, and that the second variable is time, so that the waveform represents variation in magnitude of the measured quantity as a function of time, but it will be understood that the second variable need not be time or even related to time. Typically, the oscilloscope displays a segment of the waveform during an interval containing an occurrence of a trigger event such as a zero crossing.
FIG. 1 illustrates in simplified form the architecture of a conventional digital storage oscilloscope. An analog signal under test existing at a test point 2 is applied to an acquisition system 6 through suitable interface circuitry (not shown). The acquisition system 6 includes an analog-to-digital converter (ADC) by which the analog signal is sampled and quantized. The ADC operates continuously, generating a continuous stream of digital data words and the acquisition system divides the stream of digital data words into multiple waveform records by reference to a trigger event, which is specified to the acquisition system by a processor 14. Each linear waveform record represents the time evolution of the signal under test during an acquisition interval. The waveform records are loaded into an acquisition memory 10. The processor combines the several waveform records and employs the composite waveform record to update a display memory 22. The contents of the display memory are employed to generate a waveform display on a raster scan display device 26.
The character of the display is determined by acquisition parameters which are supplied to the acquisition system by the processor 14. The acquisition parameters include the nature of the trigger event, the sampling rate, the magnitude of the conversion range of the ADC and the offset of the conversion range relative to a ground reference. Generally, the acquisition parameters can be set by user controls 18.
Oscilloscopes are frequently used by technicians who are not familiar with the capabilities of the instrument and may find it difficult to adjust the instrument to provide a clear display of the waveform. Some modem oscilloscopes have an AUTOSET function that can be invoked to aid the user in adjusting the acquisition parameters. The AUTOSET function is defined by a rule set which is stored in a program memory 30 associated with the processor 14. When the AUTOSET function is invoked, the processor 14 analyzes the data values stored in the acquisition memory and iteratively adjusts the acquisition parameters so that the length of the waveform record is approximately equal to a few periods of the fundamental frequency of the signal under test and the peak-to-peak amplitude of the displayed waveform nearly fills the screen vertically.
In many cases, the AUTOSET function is an adequate starting point for a measurement operation, but it is seldom that the display provided by the AUTOSET function will reveal signal features in sufficient detail to enable the user to make useful measurements. For example, frequently the waveform will be a nominal square wave as shown in FIG. 2 but the user will not normally want to view a complete cycle of the waveform but will want to view a detail of the waveform, such as the overshoot and ringing on the rising or falling edge, at a higher level of detail than is afforded by the AUTOSET function. Consequently, after invoking the AUTOSET function, the user must make further extensive adjustments in the acquisition parameters to obtain the desired display. In some cases, the user might not be familiar with the optimum procedure for arriving at the optimum set-up for displaying a signal feature of interest.
In accordance with a first aspect of the invention there is provided a method of operating an oscilloscope comprising (a) acquiring waveform data using a group of default acquisition parameters, (b) selecting one of a plurality of rule sets for analyzing the acquired waveform data, (c) analyzing the acquired waveform data in accordance with the selected rule set and deriving an optimized group of acquisition parameters, (d) acquiring waveform data using the optimized group of acquisition parameters, and (e) displaying the waveform data acquired using the optimized group of acquisition parameters.
In accordance with a second aspect of the invention there is provided a method of operating an oscilloscope comprising (a) acquiring waveform data using a group of default acquisition parameters, (b) analyzing the acquired waveform data using at least two rule sets and deriving at least two groups of optimized acquisition parameters, based on the rule sets respectively, (c) acquiring waveform data using the groups of optimized acquisition parameters derived in step (b), (d) separately displaying the waveform data acquired in step (c) using the respective groups of optimized acquisition parameters, (e) selecting one of the groups of optimized acquisition parameters based on the display provided in step (d), (f) acquiring waveform data using the selected group of acquisition parameters, and (g) displaying the waveform data acquired using the selected group of acquisition parameters.